Radio receivers such as AM and frequency modulation (FM) receivers are well known and are pervasive. Conventionally, these receivers have been formed of analog circuitry to receive an incoming radio frequency (RF) signal, downconvert the signal, and demodulate the downconverted signal to obtain an audio signal for output. Typically, the circuitry for AM and FM receivers, even in a combined radio, includes separate dedicated paths for AM and FM operation. While such analog-based circuitry may perform well, the area associated with this analog circuitry typically exceeds that used for digital circuitry, and the analog receivers typically include many discrete components. In contrast, digital circuitry is generally available in ever-decreasing sizes, as the benefits of advanced semiconductor processes provide for greater integration benefits. Furthermore, the cost of digital integrated circuits (ICs) is generally less than corresponding analog circuitry.
Accordingly, some radio receivers are being designed to incorporate greater amounts of digital circuitry. While such circuitry may improve performance and can be formed in small packages, typically there are complexities in processing RF signals that require significant digital processing to match the relatively simple circuitry of an analog receiver.
Additional issues exist in radio receivers. Some radio receivers include circuitry such as an automatic gain control (AGC) circuit to adjust an output level to an appropriate reference level. Because the incoming signal for an AM receiver is an AM modulated signal, any gain changes that occur rapidly (i.e., within the audible bandwidth of approximately 100 Hertz (Hz)-20 kHz) may produce undesirable noise such as in the form of audible artifacts, clicks and so forth. Accordingly, AGC circuits generally adjust gain continuously and slowly.
A receiver can include multiple amplifiers or other gain blocks, both analog and digital, within different portions of a signal processing path. While control for digital gain blocks can be adjusted slowly enough to reduce audible artifacts below a desired level, changes to analog gain blocks may occur instantaneously, producing undesired audible artifacts. Using numerous small steps that can be slowly controlled to adjust analog gain blocks may reduce these audible artifacts. However, such designs lead to excessive complexity and control, increased die size and greater power consumption.